1. Field of the Art
The present invention relates to an arrangement in an incinerator in which a fuel is burnt in a fluidized bed of refractory particles and the fluidizing air is supplied from a wind box through a perforated constriction plate supporting the fluidized bed.
2. Statement of Prior Art
Such incinerators which are also referred to as whirl pool incinerators, comprise a perforated constriction plate or nozzle plate supporting a bed of sand which is fluidized by air blowing through the perforations of the constriction plate. The constriction plate is a very important part of the incinerator structure, the object thereof being to distribute the fluidizing air when this is blown into the fluidizing bed at the underside thereof. The constriction plate is located in the incinerator plant so that on the lower side of the plate fluidizing air is blown into and pressed through the plate, whereas on the upper side of the plate there takes place a combustion at temperatures of 600.degree.-900.degree. C. Thus, substantial temperature differences will develop on either side of the plate, a fact which involves that in connection with perforated constriction plates of thermo-proof steel there will occur a heat expansion, so that the plate is bent upwardly towards the hot side.
Additionally, there also exists the possibility of unequal heating, because the rim zone of the constriction plate has a lower temperature than that which occur at the center area of the plate, a fact which contributes to an unequal heat expansion including the consequence of further bending of the plate.
Such deformations of the constriction plate entail that the fluidizing air is unevenly distributed across the constriction plate, which in turn implies an uneven height of the fluidizing bed and difficult fluidizing conditions.
Besides, large problems will occur in those cases where infeed systems for liquid fluid through the restriction plate are used, the distortions of the constriction plate inter alia effecting a deformation of the infeed system and a spraying of the liquid fuel below the plate rather than thereabove. The object of the present invention is to find a solution to the above-mentioned problems. In other words, the invention is to the effect of providing an arrangement in an incinerator having a fluidized bed, in which the problems occuring due to the heat expansion of the restriction plates during operation of the incinerator, are reduced to a minimum.